HP41 Card Reader won't read and write


I've been working on two dysfunctional card readers. I first tried
the o-ring method. I was not satisfied at all with the results
which were very inconsistent.

So I got some rubber tubing. Real rubber. I found that after
fitting and trimming the rubber tubing that now the card readers
pull the cards through very smoothly. Better that when I got them years ago.

Here is my problem. One card reader will read prerecorded cards
from HP but only after running them through many times. It will not (apparently) write and then read a card no matter how many
times I try.

The other card will not read anything.

Any suggestions?




Have you tried to clean the read/write head? In some cases, if it is too dirty, a small amount of the finest metal polisher may give some good results. Please, consider the metal polisher as a last resort. In one particular case I could only make one card reader work after a slight polishing. And try to find the one for final polishing, the least abrasive possible.

If it does not go OK, I'd follow the basic procedure: check if the read/write head wires are correctly connected, check if the contact pads in the contacts PCB are cleaned, check if the contacts of the metal strips are OK when the card passes (does the calculator generate any error messages? If so, which ones?), compare and trade parts with each other provided the card readers are of the same type (use CAT 2 and check their types: CRD RDR 1D/1E/1F/1G).

Let us know how it goes.


Luiz (Brazil)


Going to be a bit of a mother hen here, so ignore any one of these points if you have already done them

After disassembly clean all the residue from the gummy pinch roller. That means the balls, springs, platform, worm gear and card reader head, in effect, the entire mechanism. I use denatured 99% rubbing alcohol.

Now check and replace the pinch roller with the o-rings or tubing. I have had 100% success with the tubing, however, ensure the tubing is of the correct diameter iinner and outer AND that the hole is dead centre. I supplied an HCC conference attendees with such tubing with MIL specification.

Next, note the condition of the dampening couple, incorrectly named the clutch by some. The purpose of this couple is to dampen vibration generated by the motor. This may/will affect card reading. That is why I replace it at the same time with wiring insulation and why I do not just epoxy or crazy glue it. Yes the glue method has worked for some, but replicating the design standards used by HP is prudent.

Clean the contacts, ie the prongs as well as the wire to plug connections, treat with de-oxit gold. Ensure the motor works by applying a 1.5 volt current to the contacts on the motor housing.

Assemble the unit leaving the top off the unit. This allows access to the pinch roller axle with the slot in it. The key here is the pinch roller axel. It raises and lowers the pinch roller causing the card to press against the card reader head. The pressure may be too much causing binding and excessive current draw. To little and the card does not contact the reader head consistently.

Insert the card reader into an functional 41 unit. Do a cat 2 and ensure the reader is identified. Write a simple program to load to the card. Don't use a pre recorded card yet from another reader or this reader prior to the repair. The first step is to get this reader functioning for read and write prior to making it universal.

Without multitesters meters and other tech simply try to 'write' to a card. Then try to
'read'. Adjust the axel via the slot an eighth of a turn and try again. Repeat this process until you get the write function to work. If at this point you still cannot 'write' then try a pre recorded card. Once it is readable, try writing. Try minutely adjusting the axel at this point to find the sweet spot that allow both functions to work. If it is not an electronic failure this method will work.

If it is electronic; magnetized head, failed caps, corrosion affecting IC's then trouble shooting will be required.

Hope this helps.

See you in Nashville!

Cheers, Geoff

I hope this helps.

Edited: 31 July 2012, 12:25 p.m.


I supplied an HCC conference attendees with such tubing with MIL specification.

Hi Geoff,

Unfortunately I can't attend the conference, but I sure would like to have a piece of that tubing. I have searched just about every webshop but was unable to find something suitable. Of course, I will gladly pay all costs in advance. I will use it for repairing a HP-65, I assume the same tubing can be used?


Send me your snail mail. I have a roll left (50'). I will send a foot or so.


Edited: 31 July 2012, 4:33 p.m.


Hi Geoff, any chance I can buy a couple of feet of that tubing from you please ?


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